1. Field of the Invention
The present invention relates to a chelated catalyst for olefin polymerization and a method for olefin polymerization using the chelated catalyst. More particularly, the present invention relates to a chelated catalyst for olefin polymerization, including liquid-phase titanium compounds chelated by an imidazole ligand, and a method for olefin polymerization using the chelated catalyst.
2. Description of the Related Art
Efforts continue to be made to improve the properties of polymers produced by olefin polymerization in which the catalyst contains transition metal compounds. Many of these improvement efforts have focused on changing the reaction environment of the transition metal compound. Considerable advances have been made in controlling the reaction environment of the transition metal compounds by attaching cyclopentadienyl ligands to the transition metal to form metallocene compounds.
In the 1980's, homogeneous catalysts which made use of metallocene compounds drew attention for their ability to produce polymers having improved properties including high impact strength, good transparency, etc. These improved properties resulted from controlled (co)polymerization with α-olefins. Metallocene compounds were synthesized which contained derivatives of the cyclopentadienyl group such as indenyl, cycloheptadienyl, and fluorenyl groups. These cyclopentadienyl derivatives can control the electronic and stereo-spatial environment of the catalyst allowing control of the stereo-regularity and molecular weight of the polymer. The range of use of these catalysts has been expanding.
Recently, efforts have been made to develop catalysts that can produce copolymers with improved properties while also controlling granular morphology of the polymer. These efforts have focused on using heterogeneous catalysts prepared by supporting metallocene compounds on inorganic supports. For example, U.S. Pat. Nos. 5,439,995 and 5,455,316 disclose production of heterogeneous catalysts that produce polymers with excellent granular morphology and copolymer properties using zirconocene or titanocene compounds supported on magnesium or silica compounds. However, complicated organometallic chemical synthesesare typically required to produce metallocene catalysts. In addition, high-cost methylaluminoxane (MAO) or boron compounds are typically required to be used as cocatalysts. Polymers prepared by using metallocene catalysts typically have a narrow molecular weight distribution (Mw/Mn=2-5) making it difficult to process the polymer. As a result, there is a need for improved catalyst compounds that can be easily produced.
Efforts have been made to develop catalysts that can be more easily synthesized by using bidentate or tridentate chelate compounds that can produce a polymer with a narrow molecular weight distribution. Japan Patent Publication Sho 63-191811 discloses the polymerization of ethylene and propylene using a catalyst in which the halide ligand of a titanium halide compound is resplaced with a TPB ligand (6-tert butyl4-methylphenoxy). Using methylaluminoxane as a cocatalyst in the polymerization of ethylene and propylene, it was reported that a high activity catalyst was formed that produced polymers with high molecular weights (average molecular weight of 3,600,000 or more). U.S. Pat. No. 5,134,104 discloses a dioctylamine titanium halide {(C8H17)2NTiCl3} olefin polymerization catalyst. The amine ligand occupies a large volume and is used to replace a halide ligand of TiCl4. US, J. Am. Chem. Soc. No. 117, p. 3008, discloses an olefin polymerization catalyst that uses a chelated compound to provide stereochemical control of the space around the transition metal, the compound, or its derivative. The catalyst, in this case, is titanium or zirconium chelated with a 1,1′-bi-2,2′-naphthoxy ligand. Japan Patent Publication Hei 6-340711 and European Patent 0606125A2 disclose other chelated olefin polymerization catalysts for producing polymers with high molecular weights and narrow molecular weight distributions. These catalysts are formed by substituting the halide ligand of a titanium or zirconium halide compound with a chelated phenoxy group.
Olefin polymerization catalysts that use a transition metal compound chelated with an amine group have also been disclosed. Organometallics 1996, Vol. 15, p. 2672, and Chem. Commun., 1996, p. 2623 describes an olefin polymerization catalyst prepared by synthesizing a titanium compound chelated with various types of diamide compounds. J. Am. Chem. Soc., 1998, Vol. 120, p. 8640 describes a propylene polymerization catalyst using titanium and zirconium compounds chelated with diamide. These chelated compounds use MAO as a cocatalyst. All of these chelated titanium compounds and zirconium compounds were apparently introduced only for their potential use as homogeneous catalysts. No report has been published that describes a non-homogeneous chelated catalyst supported on or activated by an inorganic support in order to improve the granule morphology or copolymer properties of the resulting polymer.